Dietary and endogenously produced oxidants can disrupt normal colonocyte turnover, with implications for colon cancer etiology. Elucidation of cellular oxidation-reduction (redox) regulation of apoptosis and proliferation is therefore critical to understanding oxidant-mediated colonic cell fate, integrity and malignant transformation. Previously, we have shown that cellular glutathione/glutathione disulfide (GSH/GSSG) redox status controls apoptotic signaling, and that redox-dependent susceptibility is a function of the proliferative or differentiated phenotype. Early studies have linked mitochondrial GSH (mtGSH) loss to enhanced cytotoxicity, and oxidative mtDNA damage to increased cell apoptosis, thus underscoring the importance of the mitochondrion as a sentinel organelle in oxidative cell killing. To better understand the mitochondrial mechanisms of redox control of apoptosis, we have focused the current renewal application on: (a) the specific relationship between mt-redox status, oxidative mtDNA damage and apoptosis initiation, and (b) the physiological relevance of these processes in vivo. Our central hypothesis is that mitochondrial GSH/GSSG redox is a determinant of mitochondrial genomic integrity and together, they control the apoptotic susceptibility of colonic cells during oxidative challenge. We will test this hypothesis in three specific aims employing cell culture and mouse models and using quinones with redox cycling and/or DMA alkylating bioreactivity as models of oxidative challenge. Aim 1 will define the role of mtGSH/GSSG redox in apoptosis of normal and transformed colonic cells induced by oxidative challenge. Aim 2 will test whether mitochondrial oxidative stress and redox imbalance exacerbate oxidative mtDNA damage and attenuate mtDNA repair. Aim 3 will test the physiological relevance of oxidant-induced mtGSH/GSSG redox imbalance and mtDNA damage and repair on mitochondrial function and mucosal apoptosis in mouse colon in vivo. Given the centrality of the mitochondria in oxidant mediated apoptotic signaling, these results will yield novel information on redox control of colonic cell fate and thereby underpin the strategic development of therapeutic interventions that preserve colonic mitochondrial redox homeostasis and its genomic integrity.